Android四大组件之——Activity的开启：StartActivity()和StartActivityForResult()（图文详解）

     

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      [Android四大组件学习系列Activity篇]

       1.Android四大组件之——Activity(一)定义、状态和后退栈(图文详解)

2.Android四大组件之——Activity的生命周期（图文详解)

3.Android四大组件之——Activity的开启StartActivity()和StartActivityForResult()（图文详解）

前两次学习了Activity的基本概念和生命周期，今天学习一下Activity的跳转和值传递。

废话不多说，开始学习！

• Activity的开启

       开启一个新的Activity有两种方法:

startActivity(Intent)和startActivityForResult(Intent,int)。

startActivity(Intent):

用于开启一个新的Activity，新Activity压入栈顶。参数Intent用于描述新Activity。

startActivityForResult(Intent,int):

用于开启新Activity，新Activity退出后，返回结果给旧Activity。

startActivity好理解，startActivityForResult()就麻烦一点，下面这张图方便我们的理解:

说明一下:

requestCode,请求码,自己随意设置，但必须是非负数。只有是非负数时，Activity退出时，这个码会返回到onActivityResult()。

resultCode，结果码，用于标识返回数据来自于哪个新Activity,它的值一般是

RESULT_CANCELED, RESULT_OK， RESULT_FIRST_USER。

写了一个关于开启Activity的Demo：

共三个Activity：MainActivity用户填写用户姓名电话城市、CityActivity用于用户选择城市,ShowActivity用于展示用户信息。

MainActivity:

 package com.johntsai.startactivity;

 import android.app.Activity;
 import android.content.Intent;
 import android.database.Cursor;
 import android.net.Uri;
 import android.os.Bundle;
 import android.provider.ContactsContract.CommonDataKinds.Phone;
 import android.view.View;
 import android.view.View.OnClickListener;
 import android.widget.Button;
 import android.widget.EditText;

 public class MainActivity extends Activity implements OnClickListener {

     private Button button_city,button_phone,button_save;
     private EditText editText_city,editText_name,editText_phone;
     private static final int SELECT_CITY_REQUEST =2;
     private static final int SELECT_PHONE_REQUEST =3;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);

        button_city = (Button)findViewById(R.id.button_city);
        button_phone = (Button)findViewById(R.id.button_phone);
        button_save = (Button)findViewById(R.id.button_save);
        editText_city = (EditText)findViewById(R.id.editText_city);
        editText_name = (EditText)findViewById(R.id.editText_name);
        editText_phone = (EditText)findViewById(R.id.editText_Phone);

        button_city.setOnClickListener(this);
        button_phone.setOnClickListener(this);
        button_save.setOnClickListener(this);
     }
     @Override
     public void onClick(View v) {
          switch (v.getId()) {
         case R.id.button_city:
             Intent i = new Intent ();
             i.setClass(MainActivity.this, CityActivity.class);
             startActivityForResult(i, SELECT_CITY_REQUEST);
             break;
         case R.id.button_phone:
              Intent pickContactIntent = new Intent(Intent.ACTION_PICK, Uri.parse("content://contacts"));
              pickContactIntent.setType(Phone.CONTENT_TYPE);
              startActivityForResult(pickContactIntent, SELECT_PHONE_REQUEST);
             break;
         case R.id.button_save:
             String name=editText_name.getText().toString();
             String city = editText_city.getText().toString();
             String phone = editText_phone.getText().toString();
             Intent saveIntent = new Intent(MainActivity.this,ShowActivity.class);
             saveIntent.putExtra("content", "NAME: "+name+"\nCITY:   "+city+"\nPHONE"+phone);
             startActivity(saveIntent);
             break;
         default:
             break;
         }
     }

     @Override
     protected void onActivityResult(int requestCode, int resultCode, Intent data) {
         if(SELECT_CITY_REQUEST == requestCode){
             if(resultCode ==RESULT_OK){
                 String city = data.getStringExtra("city");
                 editText_city.setText(city);
             }
         }
         if(SELECT_PHONE_REQUEST == requestCode){
             if(resultCode == RESULT_OK){
                  Uri contactData = data.getData();
                  String [] projection ={Phone.NUMBER};
                  Cursor c = getContentResolver()
                          .query(contactData, projection, null, null, null);
                  c.moveToFirst();
                  int column =c.getColumnIndex(Phone.NUMBER);
                  String num = c.getString(column);
                  editText_phone.setText(num);
             }
         }
         super.onActivityResult(requestCode, resultCode, data);
     }
 }

 package com.johntsai.startactivity;

 import android.app.Activity;
 import android.content.Intent;
 import android.os.Bundle;
 import android.view.Gravity;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.AbsListView;
 import android.widget.BaseExpandableListAdapter;
 import android.widget.ExpandableListAdapter;
 import android.widget.ExpandableListView;
 import android.widget.LinearLayout;
 import android.widget.TextView;
 import android.widget.Toast;

 public class CityActivity extends Activity {

      private     ExpandableListView eListView;
     @Override
     protected void onCreate(Bundle savedInstanceState) {

          super.onCreate(savedInstanceState);
          setContentView(R.layout.layout_city);
          initEListView();
     }

      //初始化
      private void initEListView(){
             ExpandableListAdapter adapter = new BaseExpandableListAdapter() {

                 private String [] countries = new String[]{
                         "China","USA","UK"
                 };

                 private String [][] cities = new String[][]{
                         {"BeiJing","ShangHai","HongKong","TaiBei"},
                         {"Washington","New York","Los Angles","San Fransico"},
                         {"London","Manchester","Birmingham","Liverpool"}
                 };
                 private TextView getTextView(){
                     AbsListView.LayoutParams lp = new AbsListView.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
                             ViewGroup.LayoutParams.WRAP_CONTENT);
                     TextView textView = new TextView(CityActivity.this);
                     textView.setLayoutParams(lp);
                     textView.setGravity(Gravity.CENTER_HORIZONTAL);
                     textView.setPadding(0, 0, 0, 0);
                     textView.setTextSize(20);
                     return textView;

                 }
                 @Override
                 public boolean isChildSelectable(int groupPosition, int childPosition) {
                     Toast.makeText(CityActivity.this, "you have clicked Group:"+groupPosition+"Child:"+childPosition+"\n"+countries[groupPosition]+"  "+cities[groupPosition][childPosition],
                             Toast.LENGTH_SHORT).show();
                     Intent i = new Intent();
                     i.putExtra("city", cities[groupPosition][childPosition]);
                     setResult(RESULT_OK, i);
                     finish();
                     return true;
                 } 

                 @Override
                 public boolean hasStableIds() {
                     return true;
                 }

                 @Override
                 public View getGroupView(int groupPosition, boolean isExpanded,
                         View convertView, ViewGroup parent) {
                     LinearLayout linearLayout = new LinearLayout(CityActivity.this);
                     linearLayout.setOrientation(0);

                     TextView textView = getTextView();
                     textView.setText(getGroup(groupPosition).toString());
                     linearLayout.addView(textView);
                     return linearLayout;
                 }
                 @Override
                 public long getGroupId(int groupPosition) {
                     return groupPosition;
                 }

                 @Override
                 public int getGroupCount() {
                     return countries.length;
                 }

                 @Override
                 public Object getGroup(int groupPosition) {
                     return countries[groupPosition];
                 }

                 @Override
                 public int getChildrenCount(int groupPosition) {
                     return cities[groupPosition].length;
                 }

                 @Override
                 public View getChildView(int groupPosition, int childPosition,
                         boolean isLastChild, View convertView, ViewGroup parent) {
                      TextView textView = getTextView();
                      textView.setText(getChild(groupPosition, childPosition).toString());
                      textView.setGravity(Gravity.CENTER_HORIZONTAL);
                      return textView;
                 }

                 @Override
                 public long getChildId(int groupPosition, int childPosition) {
                       return childPosition;
                 }

                 @Override
                 public Object getChild(int groupPosition, int childPosition) {
                     return cities[groupPosition][childPosition];
                 }
             };
              eListView = (ExpandableListView)findViewById(R.id.expandableListView);
              eListView.setAdapter(adapter);
      }
 }

CityActivity

 package com.johntsai.startactivity;

 import android.app.Activity;
 import android.content.Intent;
 import android.os.Bundle;
 import android.widget.TextView;

 public class ShowActivity extends Activity {
     private TextView showTextView;
     @Override
     protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.layout_show);
          showTextView = (TextView)findViewById(R.id.textView_show);

          Intent i =getIntent();
          String content = i.getStringExtra("content");
          showTextView.setText(content);
     }
 }

ShowActivity

Demo运行效果图

                      

                        

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